1. Field of the Invention
The present invention relates to an image forming apparatus and its corresponding image forming method and process cartridge. More particularly, the present invention relates to an image forming apparatus using a cleaning blade to remove toner remaining on the surface of an image bearing member.
2. Discussion of the Background
There are known methods of electrophotography. For example, Carson Process and its variations are widely applied in photocopiers and printers. Recently, image forming apparatuses adopting electrophotography have been improved in colorization, image quality and processing speed. apparatus is widely diffused. In addition, a polymerized toner having a small particle diameter with a sharp distribution is applied in more and more cases due to its advantage in image quality. However, such a polymerized toner having a small particle diameter with a sharp distribution has a substantially sphere form so that the toner easily sneaks through between a blade and an image bearing member. Therefore, a blade cleaning system is not suitable when such a polymerized toner is used. To improve the cleaning performance for a polymerized toner, increasing the contact pressure of a cleaning blade has been considered.
When the contact pressure of a cleaning blade is increased, the amount of sneaking toner is reduced. However, the toner is excessively pressed against the surface of an image bearing member, which leads to a side-effect, such as the occurrence of filming on the image bearing member. Furthermore, abrasion of the image bearing member and the blade edge is easily accelerated, resulting in shortening of life thereof. Furthermore, this invites the increase in the rotation torque of the image bearing member, which leads to an increase in the power consumption of the image forming apparatus.
In addition, when the contact pressure of a blade is not suitable, filming occurs on the surface of an image bearing member. As the image forming process is repeated, the filming increases and causes abnormal images on the portion corresponding to the filming portion. When the filming portion increases further, a slight gap is formed in the contact portion between the blade and the image bearing member, which may lead to abnormal images such as streaks on an image caused by toner sneaking therebetween.
There are the following countermeasures to the filming which easily occurs in the case of inappropriate blade contact pressure as described above.
Unexamined published Japanese patent applications Nos. (hereinafter referred to as JOP) H05-323833 and 2001-296781 describe an image forming apparatus including an abrading blade to abrade an image bearing member. JOP H10-111629 describes a method of abrading the surface of an image bearing member with a roller having an abrasive agent.
However, in these countermeasures, not only the filming but also the image bearing member itself are abraded so that the abrasion of the image bearing member is accelerated, which leads to a shortening of the life thereof.
JOP H06-67500 describes a technology in which a toner containing an inorganic particulate and an organic particulate abrades the surface of an image bearing member. However, this technology involves the increase of toner consumption for abrasion. JOP 2001-83734 describes a technology in which an abrasive agent particulate contained in a toner abrades the surface of an image bearing member. However, the abrasive agent particulate tends to abrade the image bearing member and the cleaning blade, which may lead to a shortening of the life thereof.
Japanese patents Nos. (hereinafter referred to as JPP) 3406099 and 3514591 describe a technology in which a lubricant is coated on an image bearing member to easily remove filmed materials. When a lubricant is coated on an image bearing member, cleaning performance is improved. However, a slight amount of the toner and the external additive slips through, together with the lubricant, during the repeatedly performed image forming processes. Therefore, the abrasion of the cleaning blade is significant and the life thereof maybe shortened. Furthermore, the lubricant itself may become a binder to the external additives depending on the amount of the lubricant, which causes filming. Furthermore, the lubricant coated on the image bearing member may contaminate other processing devices, resulting in the deterioration of the function thereof.
JOP 2000-75527 describes a technology in which a lubricant is internally or externally added to a toner to improve the cleaning performance and the transfer efficiency. However, in this technology, the coating state and the coating amount of the lubricant on an image bearing member tend to vary depending on image ratio. When the image ratio is low, poor cleaning performance and filming tend to occur.
JOP 2005-62830 describes a technology in which cleaning performance is improved by applying a lubricant material to the surface layer of an image bearing member to reduce a friction coefficient thereof. In this technology, fluorine resin particulates are contained in the surface of the image bearing member and the friction charge thereof ranges from 0.2 to 0.3. However, in the typical contact conditions of a cleaning blade, a soft lubricant material is contained in the surface layer of an image bearing member and therefore, the image bearing member tends to be abraded. The durability of the image bearing member is a problem under such blade contact conditions.
To solve the drawbacks mentioned above, JOP H11-327191 describes a technology of reducing the amount of abrasion by using an image bearing member having a low friction coefficient (μ=0.4 to 0.6) to which a fluorine resin, etc. are added under the condition of reduced blade contact pressure (from 5 to 15 g/cm). However, JOP H11-327391 also describes that this technology involves a problem in that a toner may not be removed from the image bearing member having such a low friction coefficient (μ=0.4 to 0.6) under such a low contact pressure.
As described above, as to the cleaning technology using a cleaning blade for a polymerized toner having a small particle diameter, the performance of an image forming apparatus and its corresponding method and process cartridge is not satisfactory in terms of a combination of cleaning performance, anti-filming, and life length of an image bearing member and a cleaning blade.
The blade contact pressure is typically from 20 to 40 g/cm to have a margin for the cleaning performance in consideration of the fluctuation of the rubber physicality of a blade according to the temperature change and the surface property of an image bearing member. However, as a result of an intensive study by the present inventor, in the blade cleaning using an image bearing member having a friction coefficient of from 0.1 to 0.3 and a polymerized toner having a small particle diameter, it is found that it is possible to reduce the blade contact pressure without sacrificing cleaning performance when the blade condition is set in such a manner that a torque rises during removal of the remaining toner. Therefore, it is possible to elongate the life of an image bearing member and a cleaning blade. It is also found that it is possible to make the rotation torque of an image bearing member low, which leads to reduction of the power consumption and provide an image forming apparatus which can maintain a good cleaning performance over an extended period of time.